Heat radiator for projection machines



June 13, 1939. G. H. woRRALl.

ROJECTION MACHINES HEATING RADIATOR FOR P Eiled Nov. 1, 1957 2 Sheets-Sheet 1 In venan George h'. Worrall.

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l liv, n x viril/fllig June 13, 1939. G. H. woRRALL 2,152,324

HEATING Mmm-on Foa PnoJc'non canins Filed N ov. 1, 1937 2 Sheets-Sheet 2 In ventor. George ILWarraIl.

ttomey.

Patented 'June 13, 1939 UNITED STATES PATENT OFFICE HEAT RADIATOR FOB. PROJECTION MACHINES Application November 1, 1937, Serial No. 112.192

6 Claims.

This invention relates generally to motion picture projection machines. and more particularly to heat radiating means in projecting machines as typically used in the background projection method of composite motion picture photography.

'I'he background projection method of composite motion picture photography is weil understood in the art oi' motion picture photography. It consists, briefly, in projecting a background lo scene onto the rearward side of a screen, placing the action in iront of the screen, and operating the motion picture camera in front of the screen. in position to photograph simultaneously the action and those portions of the background scene projected on the screen which are not blocked out by the action. One essential requirement is that the background scene be projected on the screen with sutiicient light intensity that the exposure of the negative film in the camera to the 2o background vcomponent will not be greatly less than the exposure of the negative nim to the action. which is always brilliantly lighted. Accordingly, it is necessary to use a background projection light source of very high intensity, and this leads to extreme heating of the background projection machine. The mechanism o! the projector, especially the intermittent nlm movement and register pin mechanism, is precision made for true and accurate performance, but will not operate properly at high temperatures such as are encountered when the desired quantity Yof light is used, owing to undue expansion of heated members.

It is accordingly a primary object of the invention to reduce the heating of the projection machine by absorbed radiant energy to such an extent that a substantially increased quantity of light can be passed Vthrough the machine without exceeding allowable working temperatures.

In accordance with the present invention, a heat absorbing and radiating device is mounted on the rearward wall of the projecting machine, around the usual light entrance opening or door leading into the projector, a heat insulation member, i'or instance oi' Pyrex glass or the like.

being placed between the device and the projector. This device, which is finished dead black for eiilciency of heat absorption and radiation. is provided, in its preferred form, with tins deo lining the outer limits of the useful light beam travelling from the usual condenser lens or reflector into the machine. and intercepts all rays outside those boundaries, absorbing a large proportion o! the heat of the latter.

conducted to radiating fins on the exterior ot the This heat is l device and radiated into the, atmosphere.. The heat insulation member etlectively prevents iiow of heat from the heat absorbing and radiating device into the projector, so that the majority' oi.' the heat intercepted by the device is radiated to l the atmosphere.

As further features oi' the invention. the -rearward end of the heat radiating means and also the rearward face of the shutter oi' the projection machine are given a polished, heat refleci0 tive finish. Thus heat rays striking the rearward end of the device are reiiected back rather than climbed. while the reilectlve surface on the shutter reflects back the lightand heat during times oi movement oi' the nlm strip. l

The invention will be best understood by referring now to the following detailed description nf a present preferred embodiment thereof, rei'- ercnce for this purpose being had to the accompanying drawings, in which:

Fig. l is a side elevation of a background projection machine and diagrammatically indicatedoptical system therefor;

Fig. 2 is a fragmentary enlarged view showing a portion of the projector of Fig. l, with parts 25 broken away, and showing the heat radiator of the present invention in longitudinal vertical section;

Fig. 3 is a horizontal section taken on line 1 3 of Fig. 2; and

Fig. 4 is an elevation looking into/ the heat radiator. being a view taken as indicated by line 1 of Fig. 2.

In the drawings numeral I0 designates generally a background projection machine having nlm 35 supply magazine ii at the ,top and film take up reel i2 at the bottom. The nlm strip F, which will be' understood to carry a background scene. is taken from supply magazine Il downwardly into the body i4 of theprolection machine and 40 is guided to travel downwardly through the im guide way between vertical aperture plates i5 and I6 placedto the rear of projection lens or objective i1, the film strip having said guide way being moved and guided by any usual means to 45 enter take up magazine l2. Aperture plates I5 and i6 are provided with usual registering apertures Ilia and Ilia, respectively, each of the size of a im frame, located on the optical axis of 0bjcctive i1, and the rear housing wail I8 oi' the 50 projection machine .is provided with an aperture i I8 alined with but slightly larger 'than apertures ia and Ia. v

The nim strip is intermittently advanced by an'intermittent film movement mechanism gen- 55 erally indicated at 20, which may be of any suitable type. though l'. illustrate a preferred nlm movement of the type shown in Patent No. 1,930,723 to George A. Mitchell. This intermittent nlm movement mechanism is provided with claw pins 2l which intermittently engage the perforations at opposite edges oi' the lm strip, pull the iilm downwardly by a distance equal to a frame length, and then withdraw from the nlm to return for the next pull down. The lm is steadied at the exposure aperture by pilot or register pins 2l which engage 'the lmperforations between the times of movement of the film by the intermittent movement mechanism. Pins 24 are interconnected with the intermittent film movement in such a manner as to engage the nlm -alternately therewith. Film movement and register pin mechanism for so alternately moving and steadying the film is well known in the art. while the particular mechanism illustrated is .completely`disclosed in the aforesaid Mitchell patent, and no further description thereof is accordingly deemed necessary herein.

Objective I1 is here diagrammatically indicated as comprising a suitable lens mount 26 carrying two spaced lens components 21 and 2l, mounted within front housing wall 2l. It will be understood that objective l1 is so located with reference to the nlm frame in register at projection apertures lia andlia as to form an enlarged projection image of said frame on the background of the projection screen, not illustrated. A shutter l is provided between the aperture I9 in rear housing wall I8 and projection aperture Ita, being shown as mounted on a`rotatable shaft 3| understood to be driven in synchronism with the intermittent illm movement mechanism in such a manner as to uncover aperture i9 for the entrance of projection light each time the nlm strip comes to re and to again cover over aperture I9 just before e nlm strip is again moved by the intermittent mechanism.

The light source for the projector is diagrammatically indicated as a carbon arc A located in line with and to the rear of projection light opening I9 in the rear wall Il of the projector. A pair of condenser lenses 22 and il placed between arc A and the projector receive light from the arc and bring it to a focus at objective l1, the light rays converging from the condensers passing through opening I9 and the lm frame registered at apertures Isa and Ia to converge -to a source image located preferably between projection lens components 21 and 2B. It will be understood that the background image on the film frame registered at apertures lia and Ia, thus illuminated with light from the condensers, will be projected by objective I1 onto the background projection screen. Of course, while condensers are here shown for illustrative purposes, a reflector might equally well be used, and is to be considered the equivalent of the arrangement shown.

'I'he projector and optical system as so far described is of course of a general type well known in the art. The present invention provides a heat radiation means for dissipating the heat accompanying the non-useful portions of the condenser light otherwise received by the projection machine.

'Ihe heat radiator of the present invention comprises a casting 40, formed of aluminum or other good heat conductive material, secured to but heat-insulated from the rearward housing wall I8 of the projector. The casting is mounted on wall i8 around light entrance aperture Il, and has a converging light passing channel Il alined with said opening. Channel 4I is defined by the edges of a plurality of vertical, parallel flanges or fins I2 extending inwardly from converging top and bottom walls 4I and 4I, respectively, and converging side walls l5. The channel il dened by fins 42 coincides with the outer boundary of the useful converging light beam passing from condenserlenses 23 and Il through rear aperture or door I9, apertures lia and lBa, and comlng to a focus at the objective. Thus successive fins 42, counting from left tolright in Fig. 2, deline rectangular apertures, all similar in shape to projection apertures Ia and lia, but of progressively decreasing sizes. each of such rectangies being ofsubstantially the size and shape of the cross-sectional area of the useful light beam at that point between the condensers and objective.

The end of casting 40 adjacent housing wall i8 has a mounting ange 50, which comes against a heat insulation plate 5I having a light aperture Sla, said plate preferably consisting of Pyrex glass or other high heat resistant material of low heat conduction properties, and being mounted against wall I8, screws 52 securing the described members in assembly.

Casting 40 has external heat radiating fins B5 placed opposite internal heat intercepting fins l2.

Both the internal heat intercepting and absorbing nns I2 and the external heat radiating fins 55, as well as the inner and outer surfaces of walls Il. M and 45, are finished a full dead black, so that the emciency of heat absorption by inner ns l2, as well as of heat radiation by external fins 55, will be a maximum.

fIhe plane rearward face 60 of the radiator and the rearward face 6| 'of shutter 20 are polished and function as a heat ray reflector.

The light passed through the radiator is bounded above and below by extreme rays such as R and R', respectively, the latter being defined by the edges of fins 42, as indicated in Figs. 1 and 2.' Rays outside rays R and R' ahead of the radiator, such as rays S and S' in Fig. 1, strike the reilective surface 60 on the radiator and are reected rearwardly without substantial heat absorption. Irregular rays, such as T and T in Fig. 3, travelling at angles such as to pass outside the boundary rays R and R' within the confines of the radiator, are intercepted by iins 42 and absorbed thereby. The ordinary condenser assembly used in connection with an arc produces a substantial proportion of such nonuseful rays as T and T', and all of these are intercepted by dns and largely absorbed thereby. The heat so absorbed by the ns is rapidly conducted to radiating hns 55 and radiated therefrom into the atmosphere. The heat intercepted and absorbed by the radiator is prevented from flowing to the projector mechanism by the heat insulation plate 5I. During the time the film in the projector is being moved, the radiant energy strikes the reflective surface on the rear side of the shutter and is therefore reflected rearwardly rather than being absorbed by the shutter and conducted to the projector mechanism.

The effectiveness of the provisions of the present invention are demonstrated by the fact that the rear wall of the projector remains at a temperature approximately 100 F. below the temperature of the forward or small end of the radiator. 'Ihe device reduces the operating temamas perature oi the projector approximately 100 F. lor equal quantity oi light. or permits a greatly increased quantity ci light to be passed through the projector without increasing its temperature above a normal level. I

A projector equipped with the device of the present invention is accordingly capable of projecting a background scene on a screen at greatly increased light intensity-a result particularly desired in background projector work. It is of course to be understood that the present invention is not restricted to Ime on a projector intended solely ior background projector work, but is useful and generally applicable to any picture projection machine in which a relatively large quantity oi light must be handled, or in which heat is a problem.

i claim:

l. In combination with a projection machine having a projection aperture and means for projecting a converging beam oi' light through a film frame at said aperture. heat absorbing and radiating means disposed to thev rear oi' said projection machine, said means comprising a wall surrounding and converging with said converging light beam and provided with inwardly extending fins disposed in planes extending transversely and spaced longitudinally of said light beam. the bounding edges oi' said iins dennng said converging light beam and said ns boing adapted to intercept and absorb stray radiant energy outside the portion of said beam that passes through the nlm irame at the projection aperture. and heat insulation means supporting said heat absorbing and radiating means on the projection machine.

2. In combination with a projection machine` having a projection aperture and means ior projecting a converging beam of light through a nim frame 'at said aperture. heat absorbing and radiating means disposed to the rear of said projection machine, said means comprising a well surrounding said converging light beam and provided with inwardly extending ns disposed in planes extending transversely and spaced longitudinally oi said light beam. the bounding edges of said iins converging with and defining said converging light beam and said iins being adapted to intercept and absorb stray radiant energy outside the portion of said beam that passes through the film irame at the projection aperture. heat lnsulation means supporting said heat absorbing and radiating means on the projection machine. and a plurality ofoutwardly extending ilns on said wall formed in the planes of said inwardly extending uns and adapted to radiate heat to the surrounding atmosphere.

3. In combination with a projection machine having a projection aperture and means for projecting a converging beam of light through a iilm frame at said aperture. heat absorbing and radiating means disposed to the rear of said projection machine. said means comprising a wall surrounding and converging with said converging light beam and provided with inwardly extending black-surfaced ilns disposed in planes extending transversely and spaced longitudinally of said light beam. the bounding edges of said fins defining said converging light beam and said fins being adapted to intercept and absorb stray radiant energy outside the portion of saidV beam that passes through the nini frame at the projection aperture, heat insulation means supporting said heat absorbing and radiating means on 'the projection machine.' and a plurality of outwardiy extending black-surfaced iins on said wall formed in the planes oi' said inwardly extending iins and Vadapted to radiate heat ic the surrounding atmosphere.

4. In combination with a projection machine having a projection aperture and means for projecting a converging1 beam oi' light through a iilm frame at said aperture,`heat absorbing and radiating means disposed to the rear of said projection machine. said means comprising a wall surrounding and converging with said converging light beam and provided with inwardly extending Vblack-surfaced iins disposed in planes extending transversely and spaced longitudinally of said light beam. the bounding edges oi' said tins denning said converging light beam and saidhns being adapted to intercept and absorb stray radiant energy outside the portion of said beam that passes through the nlm i'rame ai; the projection aperture. heat insulation means supporting said heat absorbing and radiating means on the projection machine. and a heat reilective surface on the rearward end of said heat absorbing and radiating means.

5. In combination. a projection machine having a projection aperture, means i'or supporting a iilm strip at said aperture, a rotatable shutter in back of said aperture and iilm strip. a heat re-l iiective surface on the rearward side of said shutter. means for projecting a converging beam oi' light through a nlm frame at said aperture, and heat absorbing and radiating means disposed to the rear of said projection machine, said means comprising a wall surrounding and converging with said converging light beam and provided with inwardly extending fins disposed in planes extending transversely and spaced longitudinally oi' said light beam. the bounding edges of said iins deiining said converging light beam and said ns being adapted to intercept and absorb stray radiant energy outside the portion oi' said beam that passes through the iilm frame at the projection aperture. andheat insulation means supporting said heat absorbing and radiating means on the projection machine.

6. In combination with a projection machine having a projection aperture and means for projecting a converging beam of light through a film frame at said aperture. heat absorbing and radiation means disposed to the rear ot said projection and adapted to be supported thereby. said means comprising a wall surrounding and converging with said converging light beam and provided with inwardly extending iins disposed in planes extending transversely and spaced longitudinally of said light beam. the bounding edges oi said fins deiining said converging light beam and said iins being adapted to intercept and absorb stray radiant energy outside theportion oi' said beam that passes through the iilm frame atthe Aprojection aperture,-and a heat-insulation gasket interposed between the rear side oi the projection machine and the forward end oi' said heat absorbing and radiating means.

' GEORGE H. WORRALL.

cenni-'ions oF comemos. Patent No. 2,162,521 June 15. 1959.

GEORGE H. woRRALL.

It is hereby certified that error appears in the printed specification ofthe above mnbered patentrequiring correction as follows: Page 5, first column, line 14,2, claim 2, forthe word "well" read yvall; and that the said Letters4 Patent should be read with this correction therein that the seme may conform to the record of the oase in the Patent Office.

signed me sealed this la? day of August, A.' D. .1959.

Henry Van Airedale (Seal) Acting Commissioner of Patents. 

